Hepatic ischemia/reperfusion injury (IRI), an innate immune-driven inflammation response, is a major obstacle limiting the success of orthotopic liver transplantation (OLT) in patients with end-stage liver disease and those with tumors of hepatic origin. Although significant progress has been made in better appreciation of the liver inflammatory cascade by IR-stress, much less is known about its resolution, which may affect not only the severity of tissue injury itself but also, more importantly, the long-term outcomes. Recent studies document striking cytoprotective functions of hrRLX (recombinant human relaxin-2) against IR-stress in mouse OLT models via hepatocyte glucocorticoid receptor (GR) signaling; while polarizing macrophage activation via Notch1 promoted IRI-OLT resistance. These experimental findings, supported by a clinical evidence of enhanced GR/Notch1 phenotype needed for IRI resistance in human OLT, prompted to propose that rhRLX may function as a novel GR agonist and glucocorticoid (GC) mimetic in liver transplantation. Pilot studies also point to anti- fibrotic functions of the cognate RXFP1 receptor, a GR-independent RLX-2 binding partner. As the conventional murine OLT model offers a limited translational utility, this project will be dissecting GR ? RXFP1 molecular interplay in mice expressing human RXFP1 gene; as well as testing new concepts of RXFP1-driven hepatic rejuvenation of discarded human livers during hypothermic machine preservation. A newly discovered divergent role of GR?RXFP1 signaling axis in the ?acute? and ?resolution? phase of IRI-OLT inflammation, has prompted to put forth a novel and heretofore untested overall hypothesis, that: 1/ pharmacological rhRLX-induced GR enhancement will rescue OLT from acute IR-insult; while 2/ harnessing GR-independent rhRLX signaling via its cognate receptor, RXFP1, will promote homeostatic/anti-fibrotic functions in the inflammation resolution phase. Two interlocked aims explore this hypothesis:
Aim 1 : Delineate molecular mechanisms of rhRLX ? GR hepatocellular protection in OLT (acute IRI-inflammation phase).
Aim 1. 1: Test hypothesis that hepatocellular Keap1-dependent Nrf2 signaling is indispensable for rhRLX ? GR axis to prevent DAMPs release and innate inflammation in cold-stored donor livers.
Aim 1. 2: Test hypothesis that SIRT1 enhances GR-induced hepatocyte regenerative functions/autophagy in IR-stressed OLT.
Aim 2. Delineate molecular mechanisms of Notch1 / RXFP1 anti-fibrotic functions in OLT (IRI-inflammation ?resolution? phase).
Aim 2. 1: Test hypothesis that Notch1 (macrophage) ? RXFP1 (T cell) cross-regulation is essential in the resolution of IRI ? OLT inflammation.
Aim 2. 2: Test hypothesis that the activation of human RLX receptor exerts anti-fibrotic functions in the resolution of IRI-OLT inflammation in humanized RXFP1 ?knockin? mouse system.
Aim 2. 3: Test hypothesis that activation of RXFP1 receptor during hypothermic machine preservation attenuates inflammation and rejuvenates discarded human donor livers.
The shortage and poor quality of donor organs represent major limitations facing liver transplantation, the gold standard of care in patients with end-stage liver disease and those with tumors of hepatic origin. The goal of this project is to improve long-term liver transplant outcomes as well as ?rejuvenating? suboptimal hepatic tissue, and promoting homeostasis without late fibrotic pathology. Our findings should facilitate innovative interventions to improve the quality/size of the current organ supply, an absolute imperative for the full realization of success for solid organ transplantation